1. Field of Invention
The present invention relates to agricultural harvesting machines, such as combine harvesters, and more particularly to the cleaning means for separating the crop product from discardable material, such as chaff or straw particles.
2. Description of Prior Art
Commonly, combine harvesters comprise a plurality of sieves installed below the threshing concave and straw walkers for receiving the mixture of grain kernels, chaff and short straw from the threshing mechanism and separating the discardable material therefrom while guiding the kernels to a conveyor arrangement for transport to a grain tank on top of the harvester. A fan installed below the sieves assists in making the discardable material airborne and conveying it out of the harvester.
In order to optimize the effectiveness of the cleaning arrangement the mixture of threshed material has to be guided to the sieves in a uniform and even manner. Therefore a grain pan having a corrugated surface is installed below the threshing mechanism. The grain pan is linked to the sieves and is oscillated in unison therewith. The threshed material collected on the grain pan is spread out and conveyed rearwardly to the upper sieve in an even layer.
It has been experienced with certain threshing configurations such as axial flow threshing and separating systems, that the length of the grain pan is sometimes insufficient for completely leveling this layer by the time it reaches the sieves, such that one portion of the upper sieve might get overloaded while another portion might hardly be covered with the crop and chaff mixture. Then the sieve arrangement is not working efficiently as not the full sieve surface is utilized and, moreover, the wind distribution pattern of the fan is disturbed because part of the wind is escaping with no significant resistance through the low load sections of the sieves. The consequent pressure drop also affects the cleaning action on the fully loaded sieve portions. Hence, there is a need for supplementary measures in order to improve the distribution of the threshed crop material at the end of the grain pan.
It is well known in the art to provide upright dividers on the corrugated surface of the grain pan to prevent sideways movement of the crop material. This is particularly useful when the combine harvester is traveling on sideways slopes. Such dividers may also be installed at an angle to the longitudinal axis of the combine harvester to spread out a surplus of threshed material in a particular area of the combine harvester. However each divider is causing an accumulation of material along its surface such that the crop mixture is still delivered in heaps to the sieves. Different crop conditions will also require readjustment of the orientation of the deflectors for continued optimum delivery of the threshed and separated material to the sieves.
It is also known to provide guide plates or baffles between the threshing concaves and the grain pan to improve the distribution of the threshed crop material falling onto the cleaning arrangement. However when there is a major unbalance between different sections of the threshing mechanism, the guide plates have to be set at steep angles, making the system prone to plugging of the concaves.